The present invention relates in general to optical projector slides for use in optical chart projectors used by optometrists and other eye care specialists and, in particular, to a projector slide apparatus for altering the visual contrast background of the symbols or characters located on an optical acuity slide which is being projected through such optical chart projectors onto a display screen towards testing, evaluating and measuring the capabilities of a patient's eye.
For years optometrists and eye care specialists have been utilizing duplex optical chart projectors for analyzing the capabilities of a patient's eyes. Such projectors generally contain areas for insertion of two slides which, when used in combination, simultaneously project through an optical chart projector onto a screen so that a patient can read back to the optometrist what he or she was seeing on the screen. The eye care specialist would then interpret the results towards providing the patient consultation in hopes of diagnosing the patients eye deficiency and therefore bettering the patient's eye sight.
Commonly used within the optical chart projector is a optical acuity slide which contains various symbol and character charts that have different dimensions in not only height and width, but also thickness. Light is transmitted by the optical chart projector through the optical acuity slide so that the symbols or characters are projected onto a display screen. The number of symbols and characters from the optical acuity slide that the patient can read from the screen determines the keenness of the patient's eye sight. Generally speaking, the more of the symbols or characters a patient can read, the better the patient's eye sight may be.
A second slide, known as the horizontal selector slide, is used to test a patient's color perception as well as to isolate various sections of a portion of chart located on the optical acuity slide. A conventional horizontal selector slide has three apertures through which both light and the optical acuity slide may be projected onto the display means. The first aperture in such a horizontal selector slide is a substantially thin, open rectangular aperture which allows the optometrist or eye care specialist to isolate a column or vertical portion of the selected symbols or characters from the optical acuity slide as projected on the display screen. The second aperture is an open aperture utilized to project a full frame of selected portions of the selected symbols or characters of the optical acuity slide onto the display screen.
The final aperture generally found in the horizontal selector slide contains a colorized film, half of which is red and half of which is green, both of which are disposed vertically. The utilization of such film allows for a duochrome test to be performed. The duochrome test permits the optometrist or eye care specialist to test the patient's eyes for color blindness. In contrast to the vertically movable optical acuity slide, such horizontal selector slides are commonly configured for insertion and movement within optical chart projectors in a horizontal manner.
By using the two slides in combination within the optical chart projector, the optometrist or eye care specialist can test many aspects of the human eye. However, these slides do not allow for the testing or measuring of the contrast sensitivity of the patient's eye. Although not widely publicized, the contrast sensitivity of a patient's eye may be clinically significant. Contrast sensitivity testing allows the eye care specialist to detect a cataract, especially incipient cataracts, at earlier stages, as they are forming on the patient's eye. Such contrast sensitivity testing also allows for an earlier determination of when contact lenses are becoming soiled or film-coated. Both cataracts and soiled contact lenses can cause blurred vision and, in more serious cases, may lead to lack of vision.
Currently, such contrast sensitivity testing is only accomplished by providing another set of characters on the optical acuity slide. These characters are "fuzzied" or faded in varying degrees with respect to the normal characters on the optical acuity slide. In order to test contrast sensitivity of the patient, the optometrist or eye care specialist selects the fuzzied or faded characters from the optical acuity slide and projects them onto the display screen which the patient then attempts to read. However, this manner of testing patient's eye does have drawbacks. The incandescent light bulb used in most optical chart projectors does not provide a uniform amount of light to the optical acuity slide. Therefore, the light transmitted through the optical acuity slide onto the display screen may already incorporate a varying degree of contrast. The additional change of contrast embodied by the fuzzied of faded characters on the optical acuity slide has the consequence of causing any measurements taken by the optometrist or eye care specialist to be less precise. Any additional adjustments that may be made in order to compensate for the lack of precision, only makes the procedure more cumbersome and burdensome to both the eye care specialist and the patient. This difficulty in measuring the contrast of the characters as displayed on the screen has prevented the proliferation of such testing within the industry.
It is therefore an object of the present invention to provide a projector slide apparatus that can be utilized in an optical chart projector, in combination with a single optical acuity slide for use in testing the contrast sensitivity of the patient's eye--while offering a greater degree of flexibility in testing acuity diffusion distinctions in all acuity chart portions.
It is additionally an object of the invention to standardize the contrast transmission of the symbols or characters from the optical acuity slide onto the display screen.
Still further an object of the invention, is to incorporate in a single slide the contrast sensitivity testing process as well as the duochrome and other testing processes currently performed on the optical acuity slide as projected onto the display screen.
These and other objects of the invention will become apparent in the light of the present specification and drawings.